Can anyone confirm how deep a filter you can get away with on a 28/36 under the V4 bonnet? I'm probably going to use the 2bbl inlet manifold but may go with the SAH adaptor for ease/speed, at least in the interim...so ideally looking for both measurements!

That won't work so easily on a DCD because of its height, the DGV in the photo is a fair bit lower. I recently started modifying a Solex 32TDID filter housing to make it fit on a DCD, the carb needs to be recessed into the bottom part to make the filter clear the bonnet. It's a bit hard to see in the pic, but under the round plate is a ring that raises it by about 15mm, the round tin is to create extra room for the housing to clear the carb's fuel filter cap: